Means for detecting presence and movement of bodies



Sept. 4, 1951 J. L. BARKER MEANS FOR DETECTING PRESENCE AND MOVEMENT OF' BODIES Original Filed Oct. 7. 1944 2 Sheets-Sheet 1 J. L. BARKER Sept. 4, 1951 MEANS FOR DETEOTING PRESENCE ANO MOVEMENT OE BODIES Original Filed Oct. '7. 1944 2 Sheets-Sheet 2 www INVENTOR. John flr/r .Ml /l my V ReissuedSeptdtSl OFFICE MEANS FOB DETEIING PRESENCE AND 110m 0F BODIES John L. Barker, Norwalk, Conn.,

Incorporated.

Easternlndnstrlel, ofDelaware assigner to aeorporation No. 2,477,561, dated August 2,1949, Se-v rial No. 551,578, October 7, 1944. Application for reilue August 2, 19W, Serial No. 177,325

welchndhheauhnckebllappeanmtheodnalpatentbutfmnopntoftms rd-uespeeicaongmttepntedmitamdieateatheaddiommadebyrebme.

1 v This invention relates to means for determining the speed, direction.' or speed and direction of travel of vehicles along a traffic lane or track.

Embodiments of the invention may be used for determining the direction of travel and speed of travel of any vehicle having surfaces capable of reecting ultra high frequency or hyper frequency electromagnetic waves. In the description that follows, the invention will be explained with respect to its function as a speed and direction analyzing device for automotive traflic.

A number of contemporary systems provide for determining speed and direction of vehicular traflc by establishing suitably spaced stations equipped with devices for creating an electric impulse as vehicles pass by. Electrical circuits of the respective stations may be correlated in suitable apparatus to determine the time between successive impulses and thereby the speed lof transit, the spacing between successive stationsvv being known.

Such systems have utilized devices such as contactors or other switch means inthe road bed for actuation by the passage of vehicles thereover, or such means as photoelectric cells or other bedetermined. Thetimeintervalmaybeenl pressed. so to speak. in terms of "beat frequency, the magnitude of which is a function of distance of the reflecting surface from the ltransmitter-- receiver. The beat frequency, resulting from beating the reflected wave against the transmitted wave, decreases as the distance decreases, and vice versa; and by analyzing the rate of change of freqeuncy. the speed of approach or departure of the vehicle may beyascertained.

An emcient means of operation is by transniitting a frequency modulated ultra high frequency wave and beating the receivedrefiected wave against the transmitted wave. suitably amplifying the output from the transmitter-receiver, and conducting saidamplified output to non-mechanical apparatus by which an electric impulse is created by the passage of the vehicle through or within the zone Voi? effectiveness of ysuch apparatus. These prior art systems usually require direct electrical connections from the detection or impulsecreating stations to the control apparatus. Direct electrical connections are costly to install and-to maintain, and such apparatus as additionally requires excavation of the road bed is a hazard during installation and during such times as the cable or other plant must be repaired or replaced because of electrical failure.

Broadly speaking, the present invention provides for transmititng along a traflic lane or lanes an ultra high frequency of hyper frequency electromagnetic or radio wave, and means for utilizing the reflection of the wave or a portion thereof from a vehicle to detect the presence and movement of the vehicle. and to analyze its speed and direction of travel.

Itisknownthatultrahighfrequencyorhyper a aone selector" comprising a circuit tuned to a predetermined beat frequency or beat frequency range. Assuming a beat frequency characteristic Iof a distance, for example, of 300 from the refleeting object to the transmitter-receiver station, operation of a relay or meter in the output circuit of the zone selector would indicate the presence of a vehicle at that distance. As the vehicle approaches the transmitter-receiver. the beat frequency decreases; and by a suitable resistance-capacitor network, the rate of frequency change within the range of the zone selector may be translated to voltage which is a function of velocity, i. e.. speed, of the vehicle.

In short, ya voltage impulseis generated as a vehicle enters the zone defined by a tuned frequency circuit. The impulse is evaluated for direction of vehicular travel and for the speed thereof in such direction.

Subject matter relating to detection at a particular distance or in a zone corresponding to a particular range of distance per se is disclosed and claimed in my copending application Serial.

Number 535,937, filed May 17, 1944, which issued February 6, 1951. as U. S. Patent No. 2,540,089.

It will be apparent that rate of increase of the beat frequency indicates departure of the vehicle from the transmitter-receiver unit, and

frequencywavcsmaybedirectedinarelativelyv tance between the transmitter and receiver, may u celled the speed of the departure of the vehicle may be similarly analysed.

Ithasbeenfoundthatthereisasharp-Dd substantially immediately subsiding-'peak of voltage generation at the instant the vehicle enters the detection none, and as it leaves the zone. Such peak manifestations will produce false meter readings or would improperly actuate automatic signalling devices. It is a. feature of the present invention that such peaks are canout, and that the apparatus is at volt- 3 operation immediately thereafter. the vehicle'fmay be indicated on in units oi' speed, or in audible signals-which indicate a desired norm. For exinvmtion may actuate signals warning his eicess speed, or to aclevel above an unsafe low frequently desired along express right or way on n como inne beyond o preestab- 4 `a resultant voltage which is characteristic of An embodiment of the invention will now be described with reference to the several figures ot n drawings as follows:

Fig. l shows schematically a wave director unit v for directing ultra-high frequency or hyper frelished limit o: time lif the detection-apparatus l detects an approaching vehicle. How much additional time must be accorded the right of way to te the approaching vehicle depends,

obviously, upon its speed of approach. When, on a green light, a vehicle is approaching the trailic signal at a certain rate ofV speed, it is a reasonable assumption that the vehicle will maintain its speed, and the number 'of seconds between its detection at a certain dtance from the signal anditspassagethroughthesignalisreadily mechanically evaluated, and the right of way extended accordingly.

It is therefore nn object' or the invention to provide improved means for quicgly determining the speed of travel of a vehicle as it proceeds through an area or zone ona highway or other trame path.

It is another object of the invention to provide improvocmeons for the automatic determination of direction of movement of a vehicle along a trame path.

It is another object 'of the invention to provide means whereby indicating or signalling apparatus may be automatically actuated according to the speed of a vehicle in approaching or departing from a control point.

It isr still another object of the invention to through or provide means for quickly determining the speed of a vehicle whileat a relatively great distance `from a traiilc control or detection station.

It is an additional object of the invention to provide means which may be employed in conjunctionfwith trahie-actuated apparatus for allo- 'catingrlght of way along traffic lanes, to determine the `time in which a vehicle, the presence of which has been detected at a certain distance from the trame control point, maybe expected to reach said control point.

It is still another object of the invention to provide means whereby the speed of a vehicle relative to a control point may be converted to avoltage which is a function of such speed, and the voltage utilized to actuate signal or control apparatus.

It is another object of the invention to provide improved means for detecting the location of a' vehicle relative toa control point, and its speed and direction of travel, by the employment of y ultra high,i'requency or' hyper frequency radio waves.

It is an object of the invention to provide means for determining the speedoi' a vehicle by transmitting an ultra high vfrequency' radioy wave in the direction of the vehicle. beating against said transmitted wave a wave reiiected from the vehicle to obtain a beat frequency, and utilizing the rateofchangeofsuchbeatfrequencytoderive quency radio waves alongA a trafllc lane toward an approaching vehicle with a block diagram of the other major elements of a preferred embodiment of the apparatus;

Fig. 2 is a `circuit diagram of the indicator or relay circuit, and showing one means of deriving voltage proportional to speed;

Fig. 3 isa schematic representation of relays which may be employed in the' invention for actuating traic control apparatusdirection-ofmovement indicators, speed indicators, vehiclepresence indicators, and the like; and

Fig. 4 is a circuit diagramv for another means of deriving voltage proportional to frequency, employing an unbalanced multivibrator circuit.

Referring now to Fig. 1,-a vehicle IIl is illustrated travelling along a' traffic lane I2 toward the left. This vehicle may be an automobile or other ordinary'traflic element moving along a" road or highway,'and it will be assumed it is travelling along a lane or pathway near or approaching a control point from which it is desired to detect 'the presence and speed of the vehicle.

'The lane for convenience is identified at one side'of a roadway or other traillc path for two way traflic for example. The two edges of the roadway are shown by the lines I3 and Il and the center line i5 of the roadway is shown as a broken line. It is assumed that the trailic lane in which it is desired to detect vehicles is between the vedge i3 and the center line I5.

The vehicle may be detected for purpose of traffic control at an intersection of trailic lanes, for indicating or signalling the speed of the v'ehicle, for making a count or record of the number of vehicles passing within a time period, or for other purposes usual in trafilc analysis or control systems.

It will be understood that the detection zone may comprehend the entire roadway, or duplicate apparatus may be employed for the respective v approaching and departing traffic lanes.

In general, in accordance with the invention, it is desired to determine the speed of, a vehicle at some distance, or within some length of the traiic lane, which may be called a zone. In the case of street or highway trailic it may be desired in some cases to detect vehicles. and evaluate their speed, approaching at a distance of 500 feet from a traiiic intersection, or over a zone extending from 500 to 550 feet from the intersection. In other cases, the detection zones may be more advantageously located at -other disn tances from the traine intersection or control point.

At or near the intersection or other control point a transmitter and receiver unit ii is 1ocated for generating and receiving hyper frequency electromagnetic or r'adio waves of a suitable frequency. A director I1- forv these waves is arranged to direct the waves along the trame' lane in a. relatively narrow approaching vehiclell.

Fig. 1 is purely schematic, as respects the representation and location of the transmitter-receiver unit. It will be understoodthat this unit may be located at one side of the trailc lane with the transmitter unit separated from the receiver unit beam toward the 6. if desired. Also, the director I1 may be a parabolic reecfor, directional antenna array, exponential horn, or the like.

The hyper frequency oscillator and receiver and antenna therefor may be located in'a housing on or integral with a pole and the hyper frequency waves transmitted and directed by means of a wave-guide up the pole and pointed along the traillc line. or the oscillator-receiver and the wave-guide director may be closely coupled and placed in one unit on the pole or supported over the traiilc lane. I

By means of wave director I1, the hyper-frequency waves are directed along the trame lane in a substantially straight line on a narrow beam. The waves are reilected to a considerable extent from a vehicle in the line of direction of the waves and a portion of reiiected waves is received back at the wave director.

Considering briefly at first the block diagram of the apparatus in Fig. l, hyper-frequency electric wave energy is generated in the oscillator designated F. M. H. F. oscillator trans-receiver." The basic hyper-frequency waves are frequency-modulated byI the F. M. control, and

the frequency modulated waves are transmitted to the uWave director over coaxial cable or a wave guide. In the present instance it will be assumed that the F. M. waves are transmitted as electric currents over a. coaxial cable into the Wave director" where a miniature antenna transmits the electric current energy as hyperfrequency electromagnetic waves. These waves are directed by suitable means along the trame lane.

Waves reflected back from a vehicle return to the wave director, and a part of the reiected wave energy is picked up by the antenna and transmitted as electric currents to the .F. M. H. F. oscillator-transmtter-receiver."

The outgoing wave currents here are modulated by the reilected wave currents so as to provide a combined or resulting wave pattern containing a differential wave current having a frequency dependent on the difference in time required for a wave to travel out as an outgoing wave to the vehicle and back as a reflected wave. Assuming that the original waves-are frequency modulated at a substantially constant rate over the desired range, then the frequency of the differential wave resulting from combination of the outgoing and reflected waves is substantially proportional to the distance of the vehicle from the wave director, providing that the distance of the wave director from the oscillator is negligible in relation to the distance to the vehicle.

The combination of the outgoing and reected waves is connected to the detector where a rectified output is obtained characteristic of the differential frequency. This output is preferably carried through an automatic volume control amplifier designated A. V. C. amplifier" and thence through a, frequency selective circuit to an "indicator or relay, comprising an electrical network by means of which rate of change of frequency of the differential wave is converted to terms of vehicular speed for operation of indicator or relay apparatus, as later described.

The A. V. C. amplifier may be of conventional type, preferably for voltage amplification in a frequency range from 200 to 30,000 cycles for example, with one or more stages of amplification and anoutput stage. The automatic volume control factor in the amplliler is preferably only partially eifective so that the output voltage is not closely controlled but is controlled within a desired operating range and extreme variations will be avoided.

The Aoutput of the A. V. C. amplier is connected to one or more frequency selective circuits as desired. In Fig. 2 the amplifier output at wires I8, 2li is shown connected through the primary coil 2| of a pair of inductively coupled coils 2|, 22. At 23, the primary 2| is connected to the ground. A capacitor 24 is connected across the primary 2|. V

The secondary 22 of the inductively coupled coils is connected in series to capacitor 25 and thence to the grid of amplifier tube 26. Resistor 21 connects to ground as shown; Tuning capacitor 28 is connected directly across the secondary 22.

The primary 2| of the coupled coils is tuned to the desired frequency selected as representative of the distance over which it is desired to establish a zone of detection so that the presence of a vehicle within said zone causes a diiferential frequency output which is passed by the A. V. C. amplifier and then by the turned coils 2|, 22 to provide an output voltagel which may be connected to the speed-evaluating network through the illustrated output power tube 26, the cathode of which is connected to ground through the resistor 21, having capacitor 29 shunted thereacross. The plate of tube 26 is connected to power, designated B+ through resistor 30.

It will be understood by those skilled in the s art that the capacitor 2l may be made variable instead of or in addition to the variable inductance in the primary coil 2l, and also the degree of inductive coupling of the coils 2|,- 22 can be adjusted by an adjustable spacing to vary the frequency selecting characteristic.

gThe range of frequency chosen corresponds to a range of distance for the zone established along the traiiic lane. For example, a frequency range of 16,000 to 24,000 cycles may be selected as corresponding to a detection distance of 100 to 150 meters or approximately 320 to 480 feet,\

so that vehicles within this zone starting at about 480 feet from the wave director I1 and continuing to about 320 feet from the director would be within the active zone of detection. In such case the tuned circuits would be arranged for the band of frequency 16,000 to 24,000 cycles.

The selection of the most desirable band pass filter circuits for particular ranges as desired is a matter of design well known to those skilled in the art, successive stages of filter circuits being employed as desired to sharpen or broaden the frequency limits of any desired band of frequencies characteristic of the particular detection distance or zone.

In one preferred embodiment of the invention the following values may be employed and the operation of the detection apparatus will be more fully understood in a description using these values. f

Assume that it is desired to detect vehicles at distance of about 320 feet from the intersection or control point at which the wave director is located. This distance is aboutvloo meters in the metric measuring system. Now assume that the hyper-frequency waves .generated by the 7 tance of 200 meters, in of one milllonth of a second.

Now using afrequency modulation swing of 40 megacycles total, that isfrom 2980 megacycles to 3020 megacycles, varying in a saw-tooth pattern and at a rate of 600 cycles per second. the

change from minimum frequency of 2980 megacyclos to maximum of 3020 megacycles occurs in one 600th of a second or at a rate of change of 40x600=24,000 megacycles per second. The

reflected waveas received at the wave director will thus be 2 a'T-.OOOX 24,000,(l00,000- 16,000 c v cles of 16,000 cycles per second at the detector.

' thereon.

This 16,000 cycle beat wave is thus character-v 'indicative of speed of vehicular travel.

The output from "driver tube 2B is connected by conductors 3|, 32 through blocking condenser 33 to a resistance-capacitance'network comprising resistor 34 and condenser 35 shunted thereacross, and resistor 36 and shunted condenser 31. The respective resistors may be of 300,000 ohms, and capacitors 35, 31 may have values of .002 mfd. and .0005 mid. respectively. At the lower connection of resistor 36- and capacitor 31, resistor 38, of the order of 100,000 ohms, connects to ground, as shown. Lead 39 connects to the cathodeof rectifier tube 40.

The output from 26 is at constant voltage. although it will be understood that the frequency of the output is varying according to the approach or departure of the vehicle, as previously noted. Blocking condenser` 33 removes any 'direct current voltage in the output from tube' 20. The discharge from condenser 33 enters the selective resistor-capacitance network comprising resistances 34, 36 /and therewith respectively associated capacitors 35, 31.

It is well known that the reactance in ohms of v a condenser is inversely proportional to the frequency of the alternatingr current impressed It is apparent, therefore, that resistors 34, 36, and 30 constitute a voltage divider, and that the capacitors 35 and 31 oppose the passage of alternating currents in greater or less degree according to their capacities and the frequency of the currents. The capacitors therefore control the flow of current through resistors 34 and 3B, and thus control the voltage in conductor 39. In other words,the resistor-capacity network, plus the resistor 33, comprise a voltage divider whose ratio is proportional to frequency over a predetermined frequency range.

'I'he rate of change of distance of the reflecting vehicle from the transmitter-receiver-which is the speed of the vehicle-is manifested as rate of change of frequency, and therefore rate of change of voltage in conductor 39. The voltage is rectified by tube 40. Resistor 4I and capacitor 42 lter the output of tube 40.

calibrated in terms of distance, and will indicate the distance of renecting object from the transmitter-receiver.

To analyze the rate of change of voltage and thus to evaluate the speed of the vehicle, there is employed a capacitor resistor combination cornprising a .005\mfd. capacitor 44 and a 2 megohm resistor 45 in the grid circuit of vacuum tube 4G.

Ii' the vehicle is moving at relatively high speed the average voltage value applied to capacitor 44 will change relatively rapidly and more of this changing voltage will be applied to the grid` oi tube 40, whereas if the vehicle speed is relatively low, the smaller change of the averagevoltage value applied to capacitor 44 will result in said capacitor offering more impedance to current flow from this voltage, and thus a lower voltage value will be impressed in the grid.

y'I'he tube` 48, which may be considered as a thermlonic voltmeter, has the usual cathodeand anode circuit, and a meter 41, `or a voltagesensitive relay, may be connected in the circuit between the plate or anode of tube 4i and a source of D. C. positive power 48, as shown. 'I'he plus potential of source 4l is higher than that serving potentiometer 5I.

Desirably, an adjustable resistor 43 is in circuit with the meter or relay 41, as indicated. Resistance bucks the plate voltage of tube 46 to set the zero of the meter 41. Potentiometer 5| is shunted across the meter 41 for calibration thereof.

Assuming that 41 comprises a volt meter gradf uated in terms of speed, the speed of the vehicle will be indicated by deflection of the meter to the right or left of a zero center position in accordance with the rate of change of theaverage voltage value amplied by the tube- 46. The zero center position corresponds to a normal steady current value for no movement of a vehicle in of the center position relatively, showing a decreasing or increasing differential frequency respectively in the vehicle detection circuit.

It has previously been noted that there is an immediate peak reaction as the vehicle comes into and departs` from the zone of the high frequency waves. Hence, the meter 41 will have an exaggerated momentary swing upon entry of a vehicle into the high frequency wave zone, and another swing upon the vehicles leaving the zone. The steady deection of the meter between'these exaggerated swings will indicate the speed in the zone.

In an attended trafllc control station, where the attendant may discount the exaggerated momentary swings and base his reaction as to trafilc control only on the steady deflectionA of the meter between swings. the exaggerated peaks-which indicate false speeds-may be discounted. If a relay were employed instead of a meter, at 41 said relay being in circuit with traffic detection apparatus, speed signalling apparatus, or the likit is obvious that the mechanical relay could not disregard theseessentially false readings, but would immediately actuate its correlated con trol apparatus.

' For example, it is conceivable that an installation on a highway is to ash a warning signal if vehicle speeds exceed 30 M. P. H., or are less than A voltmeter 43 in the output of tube "may be 74 20 M. P. H. `The impulse of the vehicle 9 entering the speed detection zone may result in a voltage value indicative of greater than 'the 30 M. P. H. speed even though the vehicle were proceeding at between 25 and 30M. P. H. The resultingaction of the signalling apparatus would therefore be false.

The present invention embodies means comprising a monitoring circuit subject to change in amplitude of beat frequency 4for cancelling out the peak signals which occur as the vehicle comes into and departs from the detection zone.

Conductor 52 in the output of vacuum tube 26v passes through capacitor 53 and thence divides into two rectifier circuits incorporating oppositely connected rectifier tubes 54, 55. It will be noted that branch circuit 56 is connected to the anode of tube 54, whereas branch 51 is connected to the cathode of tube 55. Cathode of tube 54, and anode of tube 55 are grounded through identical resistances 50 and 59 respectively.

Connected into the cathode circuit of tube 54,

, and to the anode circuit of tube 55 are capacitor-resistance networks represented by capacifor 60 and resistance 6|, and capacitor 02 and resistance 63 respectively. Networks 60, 6| and 62. 6I correspond to the rate of change network comprising capacitor 44 and resistor 45, but work on a lower rate of change than said latter network. In advance oi' capacitors 60 and 62, a branch circuit leads to ground through the identical capacitors 64 and 65. From the capacitor resistance networks represented by 60, 6| and 62, 63 leads 66, 61 connect to the cathode of tubes 60, 10, respectively. The anodes of said tubes are grounded through appropriate resistv ances as shown. In series with each of the anode circuits of the said tubes 60, 10, is a capacitor 1|, 12, respectively, each capacitor being of equal value, preferably .01 mfd'. The respective circuits merge at conductor 13.

An amplifieri 14 may be employed to increase the sensitivity of the rectifier circuits. Through leads 15, 16, the output of amplifier 14 vconnects to the grids of the locking tubes 11, 10. Each of said locking tubes affords a path to ground, in advance of tube 46, and when either of said tubes 11, 10 is conducting, no current flows to tube 4I. and there is therefore no action of meter 41..

The threshold sensitivity of the rectifier circuit is controllable by means of a suitable source of C minus voltage,v acting through a relatively largesay 5 megohm-resistor 19. The C minus voltage sets the grid bias on tubes 11, until the bias is overcome by the output of the amplifier 14 in the rectifier circuit. Y

Condenser 53 of the rectifier circuit will have a charge impressed thereon if one rectifier tube is more effective than the other. A one megohm resistor B0 will stabilize the circuit and keep it from iioating."

The rectifier tubes 54 and 55 are subject to change of magnitude of voltage, and not` to change of frequency. A surge of voltage, either of minus or plus value, occurring as the vehicle enters or leaves the detection zone, is manifested on the grids of the tubes 11 and 10.,

Either of these tubes, depending upon the plus or minus value of the voltage in conductor 16, becomes conducting, and grounds the output from tube 40. There is no response of meter 41, therefore, until after the vehicle has entered the zone, and false meter readings are avoided.

In order to prevent a plus-voltage surge in conductor 15 from placing a plus charge on capacitor 44 due to the grid in tube 10, it is preferred to employ a rectifier tube 8| connected to V conductor 15, as shown.

Control of the characteristics of the variable vacuum tubes in the automatic volume control A. V. C., and resultant control of the gain of the A. V. C. may be accomplished by the negative output of the rectifier circuits by means of.' a conductor 02 connected between the output of tube 55 and the A. V. C., as shown in Fig. 2. It is therefore possible to obtain a relatively uniform general level of operation for variant conditions of reflection of the hyper-frequency wave.

Fig. 3 shows an organization of relays by means of which the voltages resulting from the reection from a vehicle of the hyper-frequency waves may be utilized to actuate various indicators or signals as desired.

A polarized relay is connected in parallel in the output circuit of tube 46. The voltage impressed upon the relay 90 is therefore proportional to the speed of the vehicle. Relay 90 has an armature 9| positioned between contacts 92, 93, normally in open-circuit position with respect to the said armature. The armature 9| is springbiased (not shown) 'to give to the relay,` a controlled pull-in corresponding to a predetermined speed. Actuation of the relay to close the circuit between armature 9| and contact 92 can therefore be made to result from an overspeed in one direction with respect to the control point, and correspondingly, the closing of the circuit between armature 9| and contact 93 will be effected upon an overspeed in the opposite direction. rThe leads from armature 9| and the re-l spective contacts 92, 93, may be connected to any suitable signalling lor other electrically actuated apparatus 0. S., with lamp A indicating overspeed in approach direction, and lamp D indicatng overspeed in departure" direction. Gongs or other audible signal apparatus, or other electrical apparatus may be used in lieu of signal O. S. In some instances it may be desirable to actuate an overspeed regardless of direction of movement, and in such circumstance, the leads from contacts 92, 93. may be interconnected and. a common lead taken therefrom for association with the armature lead to actuate such overspeed signalling device. v

Polarized relay 94, also in parallel electrical circuit, may be a high sensitivity relay which will pull in for any vehicle movement detected in the traffic lane. The said relay has an armature spaced between contacts 96, 91, and connection of the illustrated leads therefrom may be made v to electrical apparatus V. M. D. which will indicate the movement of a vehicle in either approach or departure direction by the respective lamps or equivalent A or D.

A second armature 90 ganged" to the armature 95 for actuation therewith is positioned between the respective interconnected contacts 99, |00, and the closing of a circuit between armature 98 and either of the contacts 99 or |00, can be made to actuate electrical apparatus V. M. which will indicate movement of the vehicle regardless of direction. f

Polarized relay |0| has armatures |02, |03 spring-biased into normally closed contact with contacts |04, |05 respectively. relay may be adjusted for a controlled pul1-infor a voltage strength corresponding to a certain low speed in the respective approach and departure directions. Pull in of the relay will open the respective armature contact circuits. For speeds which are above the pre-established minimum, the

armatures |02, |03 will be pulled out of contact with contacts |04, Ill. respectively, and there will b e no actuation of the signalling apparatus.' Should a vehicle be moving at a rate below the predetermined minimum, the spring bias of the armature maintains connection with the respective contacts. v

It will be noted that the armatures |02. |03 oi rela'y III are in series with contacts 90, 91 rerespectively oi' relay 34. A lead |00 is common to the approach signal A and departure signal D of underspeed indicator U. S. If there is no movement of the detected vehicle. relay 04 will be non-operative and. there exists an open circuit to the respective indicators of the underspeed indicator. When there is movement of the vehicle in either direction, the amature of relay 04 vcloses with contact 30 or 91 according to direction of movement, and the indicator U. S. is actuated if the vehicle speed is below the pullspeeds greater than the pull-in speed.

To detect a parked, i. e.. stationary, lvehicle in in value of relay lli, and is not actuated for the trame lane, and to actuate a parked vehicle signal P. V.. there are employed relays |01 and III. It will be recalled that meter 43, in the output circuit of rectifier tube 40 indicates the distance from the control point of a reflecting vehicle. Obviously, said vehicle will reflect the hyper frequency radio wave' regardless of whether the said vehicle is or is not in motion, and a voltage proportional to the beat frequency will appear in lead 33. Relay |01. designed to be sensitive to small voltage values, will pull in to close contact between its armature |08 and contact |03 as soon as a vehicle is detected within the detection zone.

Preferably, the relay |01 is of the vacuum tube time. although for simplification of showing, it has been conventionally represented.

Relay ill, which is in parallel with the output tion zone. If the vehicle is stationary within the zone. there will be no output from tube 46 sumcient to energize the relay III to draw its armature |I| out of contact with contact I|2 and there will therefore be a closed electrical circuit to signal P. V. On the other hand, if the vehicle `is moving within the detection zone, the output from tube 40 will energize relay H0 to pull the amature iii out of engagement with contact 2; the circuit to indicator P. V. will be open, and there'will be no actuation of said indicator. It is to be understood that in the circuit above described. the visual-indicator meter 41 may or may not-be in the output of tube 46, as desired. It will be obvious to those skilled in the art that other relays and permutations and combinations ci'4 relays may be employed to actuate-electrical devices signalling other vehicular conditions within the detection zone.

In the immediateLv foregoing description, it should vbe understood that the zero of the respective polarized relays corresponds to the zero of the voltmeter 41, as previously described.

When a vehicle is approaching the transmitterreceiver the voltage resulting from the changing beat frequency will be positive, with respect to the zero voltage of the relays, and said relays will operate. as above described, to indicate an approaching vehicle. Conversely, a departing vehicle will result in a sharp drop in voltage, the value of which will be less than the "zero" voltage of -the respective relays, and will therefore be negative with respect thereto. Departure of the vehicle will then be indicated on therespectivel signalling apparatus.

Fig. 4 discloses the use of an unbalanced multivibrator circuit for deriving voltage proportional to frequency, replacing -the resistancecapacitor combination previously described. The circuit is a modification of the familiar Eccles- Jordan trigger circuit. Triggering of the circuit results from the energy of the plus peaks of the beat frequency wave. as the discharge of the respective condensers 200, 20| reduces the negative grid voltage of whichever of the triodes 202, 203 is at the moment nonconducting, and

increases the grid voltage of the then conductv ing tube.

The triodes 202, 203 are preferably of the type commercially designated 6SN'1. 'I'he grid of tube 202 is connected through condenser 200 to the plate of tube 203, and the grid of tube 203 is connected4 through condenser 20| to the plate of tube 202.

The plates of the respective tubes are respectively given'a positive potential through the resistors 204, 205. The grid of tube 202 has a negative bias from a suitable negative potential source through a suitable potentiometer 206 and resistance 201.` The grid of .tube 203 has positive potential, applied through resistance 200.

The cathode of tube 202 leads to ground through a resistor 209, which may be 5000 ohms. Across said resistor is shunted capacitor 2|0, of .1 mfd. This resistor-capacitor combination in the cathode circuit places a voltage on the cathode which is proportional to the input voltage at conductor 3|. and sets the operating point on the` unbalanced multivibrator circuit so that it triggers only on the plus peaks of the incoming beat frequency wave.

The output from the multivibrator circuit of f Fig. 4 is characterized by a square wave pattern for the plus surges only of the beat frequency. At low frequency, characteristic of low vehicular speed, the total value of generated voltage, per unit of time, is low. For greater vehicular speeds, the average voltage value per unit of time increases in that the multivibrator circuit triggers" with increasing frequency. Thus, the voltage output of the multivibrator circuit is a function of frequency, and therefore, of vehicular speed.

As previously described with respect to the circuit of Fig. 2, the resistor-capacitor network embodying resistor 2li and capacitor 2|2 filters the output, and translates the output of the multivibrator into terms of voltage proportional to rate of change of frequency. The circuit enters capacitor 44 and thence passes into the circuit as shown in Fig. 2. w

The voltmeter 43, calibrated in units of distance from the transmitter-receiver, may be 1ncluded as shown.

Practical values for capacitors 200 and 20| may be .001 mfd. Capacitor 33 in the Fig. 4 circuit is .005 mfd. Resistor 204 can be 50,000 ohms; resistor 205, 50,000 ohms; and resistor 20B, 200,000 ohms. Potentiometer 208 has 100,000 ohms maximum resistance, and resistor 201 may be 200,000 ohms.

Whereas it is obvious that the several objects of the invention as specifically afore noted are achieved,l it is apparent that numerous changes in construction and rearrangements of the elements might be resorted to without departing from the spirit of the invention as dened by the claims.

I claim:

l. Means for analyzing a beat frequency resulting from the transmission of a linearly frequency modulated ultra high frequency radio wave along a pre-established lane and the beating against said transmitter wave of a portion of said wave reflected from a body in said lane to detect, by the value of the frequency of the beat frequency wave, the location of said body relative to the ultra high frequency transmittingreceiver station and by the rate of change of said frequency, the relative movement of said body: comprising a frequency-analyzing, means into which said beat frequency wave is fed to derive a voltage proportional to the frequency thereof said means comprising a thermionic multivibrator circuit adapted to trigger on the peaks of said beat frequency wave to afford an output characterized by a series of voltage pulses the number per unit of time ofwhich is in direct proportion to the beat frequency wave, a voltmeter in the output of said frequency analyzing means to indicate, by its reading, the distance of said body from said station; a second frequency-analyzing network to derive a voltage proportional to rate of change of frequency of said beat frequency wave, and a thermionic voltmeter in the output of said second network to indicate by the reading thereof, the rate of movement of said body relative to said transmitting-receiving station.

2. Means for analyzing the value and direction of change of the frequency of a beat frequency wave resulting from beating against an ultra-high-frequency radio wave, a portion of said wave reflected by a body in the path of said wave: comprising means for deriving a voltage proportional to said frequency of said beat frequency wave, means for deriving a voltage proportional to the rate of change of said frequency, a thermionic voltmeter circuit in the output of said last-named means, a visual indicating voltmeter in said voltmeter circuit, and means in said voltmeter circuit for establishing a zero for said voltmeter representing zero polarity of said beat frequency wave whereby `a lessening or an increasing frequency of said beat frequency wave and the rate of change of said frequency may be visually indicated by the relative deflection of said voltmeter from the zero thereof.

3. Means as in claim 2, wherein a, polarized relay is connected into the output of said voltmeter; said relay being adapted to operate signalling means remote from said voltmeter to indicate the direction of change of said beat frequency wave.

4. Apparatus for detecting the presence and motion of a vehicle within a zone of preestablished length in a traillc lane, including means for transmitting along said zone an ultra high frequency radio wave modulated over a preestablished frequency range and means for receiving and beating the portion of the radio wave reflected from said vehicle against the said modulated transmitted 'wave to derive an alternating current beat frequency wave the frequency of which is a function of the distance ofthe vehicle within said zone from the transmitterreceiving means and the increase or decrease of frequency of said beat frequency wave is representative of the direction of movement of the vehicle in saidpreestablished zone relative to the transmitter-receiver: means for obtaining a voltage the value ofv which is proportional to the rate oi' change of frequency of said beat frequency wave and the polarity of which results from the respective increase or decrease of said frequency; and a meter responsive to the value and polarity of said voltage for thereby indicating the speed of movement and direction of movement of said vehicle within said zone.

5. In apparatus for detecting the presence and motion of a vehicle in a trafllc lane, including means for transmitting an ultra high frequency radio wave along said traffic lane, said wave being linearly frequency modulated over a preestablished range, and means for receiving and beating the portion of said wave reflected from a vehicle in said traillc lane against said transmitted wave to obtain a beat frequency wave: means for amplifying the voltageY of said beat frequency wave; means for rectifyingsaid voltage; an electrical network into which said amplified rectiiied voltage is fed to derive a voltage proportional to rate of change of frequency of said beat frequency wave as the vehicle moves relative to the transmitting and receiving means; a polarized meter in the output of said network responsive .to the voltage thereof; and means for establishing a zero polarity value for said meter representing a V1stationary vehicle within said traffic lane the point of demarcation between voltages derived from respectively increasing or decreasing frequencies, whereby the voltage value and the polarity of output of said network is indicated by departure of said meter from its said zeno point will represent the rate and direction of movement of the vehicle relative to the transmitter-receiver station.

6. Apparatus for determining the rate of movement of a vehicle within a pre-established zone in a trame lane, comprising means for creating a. beat frequency wave by transmitting along said zone in the direction of said vehicle, a. linearly frequency modulated ultra high frequency radio wave and means for receiving the portion of said wave reflected from said vehicle and beating ,said reflectedy wave against the transmitted wave to derive a beat frequency wave; means for selecting an overall range of beat frequency corresponding to the respective beat frequencies resulting from wave reflection at the limits of said zone; a frequency responsive electrical network in the output of said frequency selective means forderiving a voltage proportional to the frequency of said beat frequency wave; and means for deriving from the rate of change of frequency of said wave, a voltage of one polarity for a vehicle approaching the transmitter-receiver and of a different polarity for a vehicle departing from said transmitter receiver.

'1. In apparatus for detecting the presence of a vehicle in a delimited zone ina traflic lane and for determining the speed and direction of movement of said vehicle therein by evaluating the voltage of a beat frequency wave derived from transmitting along said zone a linearly frequency modulated ultra high frequency radio wave and receiving and beating against said transmitted wave, the portion of the wave reflected from a vehicle in said zone: means for transmitting along said I of voltage correspondingto means. served by lone an ultra high frequency radio wave modulated over a preestablished frequency range and means for receiving and beating the portion of theradio wave reflected from said vehicle against the said modulated transmitted wave, means for selecting an overall range of beat frequency corresponding to the respective beat frequencies resulting from wave reflection at the limits of said zone: a frequency-responsive electrical network in the output of said frequency selective means for deriving a voltage proportional to the fre- 'quency of said beat frequency wave; a second frequency responsive electrical network for deriving a voltage value proportional to rate of change of frequency of said wave and having a polarity determined byy the increase or decrease of said frequency; means for establishing a zero polarity representing absence of change of frequency of the frequency of said beat frequency wave; and means in the output of said second-named network for indicating the value and polarity of the voltage output of said second frequency responsive network, said means being arranged to tangibly express said value and polarity in a manner indicativeof the speed and direction-of l movement of the vehicle.

8. Apparatus as in claim 7, wherein the means in the output of said second-named frequency responsive network includes relay means responsive to an increasing value of voltage the lower limit of which corresponds to a predetermined lower whose upper -limit corresponds to a speed of vehicular movement at a pre-established maximum speed, and signalling means in said relay circuit to tangibly indicate speed of vehicular movement at or below such maximum speed and the direction of movement of said vehicle.

l5. Apparatus as in claim 7, including relay a means in the-output of said first-named frequency responsive network and energized by the voltage output thereof; and signal means in cirlimit of speed of the vehicle, and signalling means served by said relay to indicate that said vehicle is moving at or above said lower limit of speed.

9. Apparatus as in claim 7, wherein the means in the output of said second-named frequency responsive network includes relay means responsive to an increasing value of voltage the lower limit of which corresponds to a predetermined lower limit of speed of the vehicle and responsive to a selected polarity of said voltage, and signailing-,means served by said relay to indicate that said vehicle is moving at or above said lower limit of speed and in a direction corresponding to the said polarity.

10. Apparatus as in claim 7, wherein the means in the output of said second-named frequencyresponsive network includes polarized relay means responsive to a range of voltage whose lower limit corresponds to a predetermined lower limit of speed ofthe vehicle and lto a relative polarity approach or departure of the vehicle within said zone, and multiple said relay to indicate that said vehicle is moving. in an approach or departure direction relative to the ultra high beating the reflected cuit with said relay means and actuated thereby to' indicate the presence of a vehicle in said zone.

16. Apparatus for the detection of movement, within a delimited zone, of a body having wavereflective properties, by evaluating the beat frequency derived from a linearly modulated rultray high frequency wave projected against said body in its path of movement within said zone and portion of said wave against said transmitted wave: comprising means for filtering said beat frequency to derive a range of beat frequency comprehending the respective beat frequencies corresponding to wave reflections from the respective limits of said zone; means includng [passing said beat frequency wave into] a frequency responsive electrical network'to derive from said beat frequency range wave a voltage proportional to the frequency of said wave;

q means for [amplifying and] rectifying the outfrequency transmitter-receiver, at or above said lower limit of speed.

11. Apparatus as in claim 7, wherein the means in the output of said second-named frequency responsive network includes relay means responsive to a value of voltage output of said network indicative of movement of said vehicle within said zone at any speed at or above a predetermined lower limit of speed.

l2. Apparatus as in claim 7, wherein the means ln the output of said second-named frequency responsive network includes relay means responsive to a value and polarity of voltage output of said network'indicative of direction of movement of said vehicle within said zone at any speed at or above a predetermined lower limitof speed.

13. Apparatus as in claim 7, wherein the means in the output of said second-named frequency responsive network includes polarized relay means put of said( network, means including [and passing said amplified and rectified output into] a second frequency responsive network to derive from said rectified output a voltage responsive to rate of change of frequency of said-wave; means for indicating movement of said body according to voltage value input; means responsive to the voltage output of said second-named network to actuate said indicating meansv lvalue of the output of said second-named network]; and means responsive to-sudden large increase and decrease in amplitude of such beat frequency range wave accompanying entry and departure of the body into and ,from said zone respectively for by-passing in advance of said indicating means, the voltage corresponding to the apparent peak rate of change of the frequency of the beat frequency range wave resulting as the body entersfand leaves said zone, whereby said indicator means will not be actuatedby such lastnamed voltage. 1' y 17. Apparatus as in claim i6 wherein the voltage 'by-passing means comprises a rectifying system connected to said rst beat frequency responsive means and including vacuum tubes connected into the output of said second-named frequency responsive network and individually rendered conductive to ground in advance of said indicator means according to whether a positive or negative voltage results from the peak change of the amplitude of the said beat frequency range wave.

1s. Apparatus m man 1s, wherein the vou'- polarized relay meansl responsive to a range of voltage of said output' [for indicating movement of said body according to the voltage age lay-passing means comprises a rectifylng system shunted across said second-named frequency-responsive network and including vacuum tubes respectively reversely connected into the output of said second-named frequency responsive network and individually rendered conductive to ground in advance of said indicator means according to whether a positive or negative voltage. resulting from the peak changes in amplitude corresponding to said peak beat frequencies is impressed kupon the respective vacuum tubes. to provide a path to ground for the voltages derived from said peak beat frequencies.

19. Apparatus for detection of presence and direction of movement of vehicular traffic Within a. preestablished zone in a traflc lane, comprising means for transmitting modulated ultra high frequency waves along said tramo lane and for receiving a portion of said Wave reflected from a vehicle in said zone and for beating said reflected wave against said transmitted Wave for obtaining a beat frequency wave; means for deriving a direct current output voltage indicative of the rate of change of frequency of said beat frequency wave; means for identifying the polarity of said voltage as represented by Whether the frequency of said beat frequency wave is increasing or decreasing corresponding to direction of movement of said vehicle; polarized relay means operated by said derived voltage; and a work circuit controlled by said relay means.

20. Apparatus for detection 'of presence and direction of movement of vehicular traflic within a preestablished zone in a traffic lane. comprising means lor transmitting modulated ultra high frequency waves along said trafc lane and for receiving a portion of said wave reflected from a vehicle in said zone and for beating said reiiected wave against said transmitted wave for obtaining a beat frequency wave; means for deriving a direct current output voltage indicative of the rate of change of frequency of said beat frequency wave; relay means operative only by a predetermined polarity of said output voltage corresponding to one direction of movement of said vehicle; and a work circuit controlled by said relay means.

21. Means for analyzing a beat frequency resulting from the transmission of a linearly frequency modulated ultra high frequency radio wave along a pre-established lane and the beating against said transmitted Wave of a portion of said wave reflected from a body in said lane to n detect, by the value of the frequency of the beat frequency wave, the location of said body relative to the ultra high frequency transmittingreceiver station and by the rate of change of said frequency, the relative movement of said body: comprising a frequency-analyzing means into which said beat frequency wave is fed to derive a voltage proportional to the frequency thereof, said means comprising a pair of thermionic tubes arranged in an unbalanced multivibrator circuit the triggering voltage thereof being provided by the beat frequency wave; the cathode of the first tube of the pair being connected to ground through a resistor and thereacross shunted capacitor having respective values such that the cathode voltage of said tube is proportional to the beat frequency voltage; a voltmeter in the output of said frequency analyzing means to indicate, by its reading, the distance of said body from said station; a second frequencyanalyzing means whereby to derive a voltage proportional to rate of change of frequency of said beat frequency wave. and a voltmeter in the output of saidlsecond means to indicate by the reading thereof, the rate of movement of said body relative to said transmitting-receiving station. I

22. Apparatus for detecting the presence and movement of vehicles within a predetermined area iii a trail-ic lane, comprising means for transmitting along said areal an ultra high frequency radio wave modulated over a preestablished frequency range and means ior receiving and beating the portion ol' the radio wave reiiected from a vehicle against the modulated transmitted wave to derive an alternating current beat frequency wave trie frequency ot Whicnvis a function oi the distance of trie vehicle within said ai'ea from the transmitter-receiver means and the increase or decrease of frequency of said beat frequencywave is representative of the direction of movement of tne vehicle with respect to said transmitter-receiver; means for dei'iviiig a voltage proportional to tne frequency or the beat irequeiicy wave; means for obtaining a voltage proportional to the rate o1 ciiange of frequency of tne beat frequency wave; a signal foi' indicating Elle presence 0I 3. VEIllUie il] Salo. area; and an electric circuit for actuating said signal only if said vehicle is stationary, comprising a relay energized Dy the voltageoutput of said first-named voltage deriving means and adapted to close a normally open switch in said signal circuit upon energization of said relay and a second relay energized by said second-named voltage deriving means and adapted to open a normally closed. switch in said signal circuit upon lenergia-ation of said relay; whereby if both of said relays are energized the said signal will not operate but if only the first relay is energized the signal will operate.

Z3. Apparatus for the detection of movement, within a delimited zone, o] a body having wavereflective properties, by evaluating trie beat frequency derived from a linearly modulated ultra high. frequency wave proyectea; against said body in its path of movement within said zone and beating the reflected portion of said wave against said transmitted wave: comprising means for filtering said beat frequency to derive a range of beat frequency comprehendi'ng the respective beat frequencies corresponding to wave reflections from the respective limits of said zone; means for amplifying said beat frequency range wave; means including a Jrequency responsive electrical network to derive from said beat frequency range wave a voltage proportional to the frequency of said wave; means for rccti'fyi'ng the output of said network, meansA including a second frequency responsive network to derive from said rectified output a voltage responsive to rate of change of frequency of said wave; means for indicating movement of said body according to voltage value input; means responsive to thevoltage output of said second-named network to actuate said indicating means; and means responsive to sudden large increase and ldecrease in amplitude of'such. beat frequency range wave accompanying entry and departure of the body into and from said zone respectively for by-passing in advance of said indicating means, the voltage corresponding vto the apparent peak rate of change of the frequency of the beat frequency range wave re-` sulting as the body enters -and leaves said zone, whereby said indicator means will not be actuated by such last-named voltage.

amos

24. Apparatus for the detection of movement, within a delimited zone, of a body having wavereflective properties, by evaluating the beat frequency derived from a linearly modulated ultra high frequency wave profected against said body in its path of movement within said zone and beating the reflected portion of said wave against said transmitted wave: comprising means for fltering said beat frequency to derive a range of beat frequency comprehending the respective beat frequencies corresponding to wave reflections from the respective limits of said zone; means for deriving from said beat frequency range wave a voltage proportional to the frequency of said wave, means for deriving from saidsvoltage a further voltage responsive torrate of change of frequency of said wave; means for indicating movement of said body according to voltage value input. and means responsive to said further voltage to actuate said indicating means; and means responsive to sudden large increase and decrease in amplitude of such beat frequency range wave accompanying entry and departure of the body into and y from said zone respectively for by-passing in advance of said indicating means, the voltage corresponding to the apparent peak rate of change of the frequency of the beat frequency range wave resulting as the body enters and leaves said zone,

whereby said indicator means will not be actuated by such last-named voltage.

25. Apparatus for the detection of movement,

within a delimited zone, of a body having waverefiectivejproperties, by evaluating the beat frequency derived from a linearly modulated ultra high frequency wave projected against said body in its path. of movement within said vzone and beating the reflected portion of said wave against f said'transmitted wave: comprisingV means -for yfiltering said beat frequency to derive a range of beat frequency comprehending the respective beat frequencies corresponding to wave reflection from the respective limits of said zone; means for trolled by the last named voltage pulses from such networks to actuate said grid controlled electronic tube means to render the latter conducting to ground during and in response to such voltage pulses,.whereby said indicatorA means will not be actuated by voltage pulses corresponding to the apparent. peak rate of change of frequency of the beat frequency range wave resulting as the bodyenters and leaves said zone.

26. Apparatus as in claim 25, in which said grid controlled electronic tube means includes tubes having anode-cathode circuits oppositely connected/between said output and ground and having grids connected in common, and means normally biasing said grids to render said tubes nonconducting; and in which said rectifier networks comprise rectifier and series resistance circuits connected in parallel between the input of said first voltage deriving means and ground with such circuits oppositely polarized, and a shunt capacitor across the output of each of said rectifiers and a series capacitor and resistance across the output of each of said rectifiers with another Y,

rectifier and resistor across the last named resistance, to derive positive and negative voltage values respectively from the respective rectifier circuits dependent upon such sudden large changes in amplitude of said beat frequency range wave corresponding to peak rate of change of the voltage output of said first voltage deriving means, and series capacitors in the outputs of the respective last named rectifier-resistor circuits todierentiate such output to provide control output voltage pulses for very rapid changes deriving from said beat frequency range wave a voltage proportional to the frequency of said wave, means for deriving from said voltage a further voltage responsive to rate of change of frequency of said wave; means for indicating movement of said body according to voltage value input; means responsive to said further voltage to actuate said indicating means; grid controlled electronic tube means connected between ground and the output of said further voltage deriving means at a point between said output and said indicating means for shunt-ing said further voltage to ground and away from said indicating means when said grid controlled electronic tube means is rendered conducting, and two oppositely conducting rectifying networks connected to the input of the first frequency proportional voltage deriving means to derive voltage pulses of Opposite polarity in ref sponse to sudden large changes in amplitude of said beat frequency range wave applied thereto corresponding to sudden changes in such frequency proportional voltage as said body enters Number Name Date 2,188,293 Williams Jan. 23, 1940 2,206,896 Higgins July 9, 1940 2,232,858 Lane Feb. 25, 1941 2,268,587 Guanella` Jun. 6, 1942 2,301,929 Budenbom Nov. 17, 1942 2,337,328 Hathaway Dec. 21, 1943 2,362,503 Scott Nov. 14, 1944 2,402,484 Suter June 18, 1946 2,403,755l Rankin L July 9, 1946 2,409,560 Haight Oct. 15, 1946 2,453,169 Varian Nov. 9, 1948 2,454,673 Sanders Nov.` 23, 1948 2,467,455 Aurell vApr. 19, 1949 2,485,583

and leaves said :one respectively; and means conin the last named voltage values characteristic of a body entering and leaving said zone respectively. and means for applying such last named voltage pulses to the control grids of said grid controlled electronic tubes to reduceI momentarily -their grid bias to render such tubes conducting to by-pass to ground said further voltage output during such peak voltage pulses.

JOHN L. BARKER.

REFERENCES CITED UNITED STATES PATENTS Ginzton .v oct. ss, 1949 

